As processes for producing an α,α-bis(hydroxymethyl)alkanal, a process for allowing an aliphatic aldehyde to react with formaldehyde in the presence of a basic catalyst is known. Examples of the basic catalyst used in the process include hydroxides such as sodium hydroxide, potassium hydroxide, and calcium hydroxide, containing an alkali metal or an alkaline-earth metal; carbonates, such as sodium carbonate, potassium carbonate, sodium hydrogen carbonate, and potassium hydrogen carbonate, containing an alkali metal or an alkaline-earth metal; tertiary amines; and solid basic catalysts such as basic ion exchangers (see, for example, Japanese Published Examined Patent Application No. 20965/1977, Japanese Published Unexamined Patent Application No. 263141/1987, Japanese Published Examined Patent Application No. 55181/1992, U.S. Pat. No. 3,312,736, and West Germany Patent No. 2,507,461).
In the production of the α,α-bis(hydroxymethyl)alkanal, the yield of the α,α-bis(hydroxymethyl)alkanal is low in general when the ratio of formaldehyde to the aliphatic aldehyde is less than or equal to a stoichiometric ratio, that is, the amount of formaldehyde used is 2 mol or less with respect to 1 mol of the aliphatic aldehyde. Therefore, processes in which two moles or more of formaldehyde is allowed to react with one mole of the aliphatic aldehyde are disclosed (see, for example, Japanese Published Unexamined Patent Application No. 135717/1979 and Japanese Published Examined Patent Application No. 55181/1992). However, the processes disclosed in these patent documents are not cost-effective because a large amount of formaldehyde remains after the completion of the reaction and complicated operations for separating and/or recovering the remaining formaldehyde must be performed. Furthermore, if a reaction product is subjected to a step such as an oxidation step or hydrogenation step without removing the remaining formaldehyde, the processes have problems such as a necessity for an excessive amount of reactants and a heavy load of a step of refining a product.
On the other hand, a process in which formaldehyde is allowed to react with an aliphatic aldehyde at a stoichiometric ratio is also disclosed (see, for example, Japanese Published Unexamined Patent Application No. 209323/1999). However, an example disclosed in this patent document shows that the conversion of formaldehyde is below 90% and a step of removing formaldehyde is necessary. If formaldehyde is not removed, there is a problem that the load of a refining step becomes heavy.
Accordingly, a process for producing for enhancing the conversion of formaldehyde to produce an α,α-bis(hydroxymethyl)alkanal efficiently has been demanded.